JPH0226538B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for producing fine particles by causing a thermal excitation reaction of raw materials that do not react at room temperature using dielectric breakdown plasma generated by focusing laser light.

<Conventional technology> In recent years, fine particles (100
The utility value of microparticles (on the order of Å) is increasing, and the demand for manufacturing technology for such microparticles is increasing.

Conventionally, the following techniques are known as techniques for producing such fine particles.

(i) Method using excitation by absorption of laser light
CO ₂ −Transversely Excited Atmospheric
Laser (hereinafter simply referred to as CO ₂ −TEA laser)
Using gaseous molecules as raw materials that have a strong absorption band in the wavelength band (approximately 10 μm),
The raw material is irradiated with CO ₂ -TEA laser light, molecules are reacted by absorption excitation, and fine particles are generated.

(ii) Method using DC arc plasma Raw materials are introduced in gaseous form into the flame of DC arc plasma, which has a high temperature of 10 ⁴ K or higher, undergoes a thermally excited reaction, and is then rapidly cooled to generate fine particles.

(iii) Method using evaporation in low-pressure gas The metal in the crucible is heated and evaporated in low-pressure gas, and the evaporated metal molecules collide with the molecules of the low-pressure gas to release energy and cool the metal. Generates molecular gas, which is condensed to produce fine particles.

<Problems to be Solved by the Invention> In the method (i) above, since the reaction is based on absorption excitation, the absorption band is CO ₂ - as in SiH ₄ etc.
Only molecules that are strong in the TEA laser wavelength band or have a broad absorption band can be used as raw materials, and there are restrictions on the types of raw materials. By using different powerful lasers in the visible to ultraviolet range, the range of raw materials that can be used can be expanded, but CO ₂ −
It is extremely disadvantageous in terms of power efficiency compared to TEA lasers.

Further, in the method (ii), a large amount of electric power is required to generate DC arc plasma, and it is difficult to stabilize this plasma. Furthermore, there have been cases where electromagnetic effects interfere with introducing the raw material into the plasma.

Furthermore, in the methods (ii) and (iii), the thermal inertia is large, so the desired temperature zone cannot be created in a short time and within a limited range, resulting in poor controllability.

The present invention was made in view of the conventional circumstances as described above, and is an apparatus for producing fine particles using a novel method in which a dielectric breakdown plasma is generated by a laser beam focused by a lens, and a raw material is caused to undergo a thermal excitation reaction by this plasma. The purpose is to provide

<Means for Solving the Problems> The structure of the particle manufacturing apparatus according to the present invention is to introduce a gaseous raw material into a tubular passage, irradiate a laser beam from a laser source along the axis of the tubular passage, and In the particle manufacturing apparatus, the laser beam is focused in the tubular passage by a lens to generate dielectric breakdown plasma near the focal point, and the raw material is generated into fine particles by a thermally excited reaction caused by the dielectric breakdown plasma, wherein the tubular passage is made of a porous material. A member is used to send an inert gas into the passage through the porous member, or an air chamber is formed on the upstream side of the tubular passage, and the inert gas is directed from the air chamber along the passage wall surface. The sink or the tubular passage is vertically extended, an oil chamber is formed in the upper part of the tubular passage, and silicone oil is caused to flow down from the oil chamber along the inner wall surface of the passage. .

<Operation> Dielectric breakdown plasma induced by laser light is generated in a limited range near the focal point of the lens. For this reason, the gaseous raw material introduced into the plasma is rapidly heated to an extremely high temperature within the plasma to generate fine particles, and then the fine particles are transferred to the outside of the plasma or the plasma is extinguished, causing the fine particles to rise to an extremely high temperature. It is rapidly cooled and stabilized, and its particle size becomes constant. Further, the particle size of the fine particles can be easily controlled by temperature control by adjusting the flow rate and concentration of the gaseous raw material or the plasma generation area.

Here, since the irradiation direction of the laser beam is along the axis of the tubular passage, the dielectric breakdown plasma is generated in a cylindrical area along the axis. When a porous member is used as a tubular passage, when an inert gas is fed into the passage through the porous member, an inert gas layer is formed on the inner wall of the passage, and the plasma and the inner wall of the passage are combined. becomes isolated. Therefore, particulate deposition and damage to the tubular passages are effectively prevented.

Even if an air chamber or an oil chamber is provided instead of using a porous member as the tubular passage and an inert gas or silicone oil is flowed therein, the same result will be obtained.

<Examples> Examples of the present invention will be described below with reference to the drawings.

First, the apparatus for producing fine particles of the present invention will be explained with reference to FIG. 1, which schematically shows the structure thereof. The fine particle manufacturing apparatus has a container in which a raw material container 1 and a product container 2 are communicated with each other through a cylindrical tubular passage 3. Raw material container 1
Gaseous raw materials (hereinafter referred to as raw material gas) A and B are introduced into the container 1, and these raw material gas A and raw material gas B are mixed by a fan 4 within the raw material container 1. Note that these raw material gas A and raw material gas B are a combination that does not react even if mixed at room temperature. The pressure in the product container 2 is set to be lower than that in the raw material container 1, and the mixed gas of raw material gas A and raw material gas B passes through the tubular passage 3 at a certain flow rate to form the product from the raw material container 1 side. It is designed to flow towards the container 2 side. The raw material container 1 is provided with a window 5 facing the opening on one end side of the tubular passage 3, and the CO ₂ -TEA laser beam from the laser oscillator 6 is focused by a lens 7 and enters the container through the window 5. I'm starting to focus on 3. Furthermore, these windows 5
The lens 7 is made of KCl, NaCl, Ge, etc., which are transparent at the wavelength of the CO ₂ -TEA laser.
There is no particular limitation on the material as long as the laser light used, such as the CO ₂ ^- TEA laser, passes through it.

The CO ₂ -TEA laser beam from the laser oscillator 6 is approximately 0.5 to approximately 1 J/pulse class, and the pulse duration is approximately
1μs, peak output approximately 1MW, and lens 7
The ultra-strong electromagnetic field causes an ionization effect near its focal point, creating a laser-induced dielectric breakdown plasma within the tubular passage 3.
Breakdown Plasma (hereinafter referred to as LIDB plasma) is generated. For example, 0.6~0.8J/pulse
Approximately 2 cm in length and 1 mm in diameter with CO ₂ -TEA laser beam
LIDB plasma P is generated, LIDB plasma P
volume (approximately 0.02 cm ³ ≒ 2 × 10 ^-6 mol) and the specific heat of the gas (as a diatomic molecule) (7 Cal/mol・K ≒
30Cal/mol・K) and LIDB plasma P is approx.
It has an extremely high temperature of 10 ⁴ K. This high-temperature state is thought to relax on the order of milliseconds, and as a shock wave is observed, a thin cylinder of rapidly expanding high-temperature gas remains inside the tubular passageway 3, and immediately afterward, it rapidly cools down within about 10 milliseconds due to expansion and radiation. do.
That is, at a predetermined time according to the pulse of the laser oscillator 6 and at a predetermined place according to the focus of the lens 7.
A rapid heating state of as much as 10 ⁴ K (10 ¹⁰ K/s) and a rapid cooling state of dropping at 10 ⁵ to ^{10 7} K/S can be obtained in a short time of about 1 μs. This state has a much higher frequency (CO ₂ −
Assuming the TEA laser wavelength is 10 μm (3×10 ⁸ m/
s)÷(10×10 ⁻⁶ m)=3×10 ¹³ Hz) can be repeated at about 100 pps. Note that the present invention can also use a continuous wave laser, and in the case of a continuous wave laser, unlike the above pulsed laser, the rapid cooling is performed by moving it outside the generation area of the LIDB plasma P.

According to the fine particle manufacturing apparatus having the above configuration, the raw material gas A and the raw material gas B mixed in the raw material container 1 flow through the tubular passage 3 to the product container 2 side.
This mixed gas is transferred to the LIDB plasma P in the tubular passage 3.
Fine particles are generated due to thermal excitation reaction due to rapid heating caused by
The fine particles generated by rapid cooling due to the extinction of the LIDB plasma by the pulse laser are transferred to the product container 2 while retaining their shape without undergoing any further reaction. Specifically, even if it is usually mixed as a raw material,
When using SnCl ₄ gas and O ₂ gas, which only react at temperatures above 1000°C, Cl ₂ gas and fine particles
SnO ₂ is obtained and other halides, e.g.
The same applies to SbCl ₅ , AlCl ₃ , FeCl ₃ , TiCl ₄ and the like. In addition, nitrides that are gaseous at room temperature,
Borides, carbides, etc. can also be used as raw materials. Furthermore, a raw material such as FeCl ₂ can be evaporated and condensed in an inert gas to create an aerosol, mixed with other raw material H ₂ gas at room temperature, and reacted with LIDB plasma P to form particulate Fe and HCl gas. You can also get

According to the present invention, fine particles can be produced from an extremely wide variety of raw materials, such as a combination of aerosol and gas as well as a combination of aerosols and the like. Furthermore, it is of course possible to supply two or more kinds of raw material gases into the raw material container 1, or these raw material gases may be mixed in advance and supplied to the raw material container 1.

Here, when the CO ₂ -TEA laser pulse is 50 pps, the length is 2 cm in the tubular passage 3 with a diameter of 2 mm.
Since the flow rate of the raw material gas that passes through the area of the LIDB plasma P in 1/50 s is 1 m/s, the throughput is 3 cm ² /s, and 1 mole of the raw material gas is passed through the LIDB plasma at 1 atmosphere. It turns out that it takes about 2 hours to process. This means a production rate of the order of 10 g/hr, which is relatively efficient compared to other currently known production methods. For example, in the case of SnCl ₄ gas + O ₂ gas → SnO ₂ fine particles + 2Cl ₂ gas, from a total of 2 moles of raw material gas
150.7g of SnO ₂ fine particles are generated, for example, the pressure inside the container is reduced to 200torr, and the raw material gas is 50% Ar gas.
Even if diluted to 5g/hr, fine particles can be produced on the order of 5g/hr.

Furthermore, assuming that the condensation during the process of rapidly cooling fine particles generated by LIDB plasma can be described by the aerosol coalescence aggregation theory, the average volume of fine particles ∝ (residence time) ^6/5 (volume concentration) ^6/5 (absolute temperature) is ^3/5 , so the average particle diameter p∝ (partial pressure of raw material gas/flow rate of raw material gas) is considered to be ^0.4 (however, the absolute temperature is determined by the laser beam and there is no excess in the reaction system ^. (assumed not dependent). Therefore, in order to obtain fine particles with a smaller diameter, the partial pressure of the source gas may be lowered (the concentration of the source gas may be lowered) or the flow rate of the source gas may be increased. However, when LIDB plasma is induced by a pulsed laser, in order to cause all of the raw material gas flowing in the tubular passage 3 to react with the LIDB plasma, a restriction is imposed on the flow rate of the raw material gas. For this reason, when using a pulsed laser, it is easy to control the particle size of the generated fine particles by controlling the partial pressure of the raw material gas, but in this point it can be said that particle size control can be performed more easily if a continuous wave laser is used. In reality, the particle size of the generated fine particles is much more dependent on the raw material gas partial pressure than on the raw material gas flow rate, so by controlling the raw material gas partial pressure, even with a pulsed laser, the particle size can be reduced from about 20 Å to approx.
It was confirmed through experiments that the particle size could be sufficiently controlled within the range of 2000 Å.

As mentioned above, if the diameter of the tubular passage 3 is made as small as the diameter of the LIDB plasma, there are the following advantages.

(a) Since all the raw material gas passes through the LIDB plasma, the generation efficiency of fine particles is high.

(b) Since the gas flow in the tubular passage is unidirectional, backflow from the product container 2 to the raw material container 1 is prevented and regrowth of particulates is prevented.

(c) Since the raw material container 1 and the product container 2 are substantially separated, for example, the raw material chamber is heated above the condensation point,
By putting liquid nitrogen into the product container 2 to create a difference in temperature conditions between the two, or by setting the raw material container 1 at high pressure and the product container 2 at low pressure to create a difference in pressure conditions between the two, It is possible to easily set conditions such as adding a gaseous substance that adsorbs to the surface of the fine particles generated only in the container 2 and modifies the surface.

Here, when the tubular passage 3 is made small in diameter as described above, while there is the above-mentioned advantage, the generated fine particles may be thermally deposited on the wall surface of the relatively low-temperature tubular passage 3, and the radial direction of the LIDB plasma may It is conceivable that the tubular passage 3 may be damaged due to the rapid expansion of It is possible to reduce thermal deposition of particulates by rapid expansion cooling into the material container 2. On the other hand, in order to more effectively prevent thermal deposition of particles and damage to the tubular passage 3, the diameter of the tubular passage 3 may be reduced, although the part near the wall surface of the tubular passage 3 will not be turned into plasma, resulting in a slight drop in particle generation efficiency. Just make it as thick as possible.

The structure shown in FIGS. 2 to 4 maintains the advantage of the small diameter of the tubular passage 3 without reducing the particle generation efficiency, and effectively prevents thermal deposition of particles and damage to the tubular passage 3. This is an example.

In the system shown in FIG. 2, the tubular passage 3 is divided into a raw material container side portion 3a and a product container side portion 3b, and both of these portions 3a and 3b are connected to a cylindrical passage having a porous member 3d such as a glass filter. Joint member 3
c, and at least a portion of the tubular passage 3 surrounding the generation area of the LIDB plasma P is made larger in diameter than the diameter of the LIDB plasma. Note that 8 in the figure is an O-ring for sealing. Inert gas such as Ar is supplied from a supply source (not shown) into the joint member 3c and is evenly supplied around the LIDB plasma P in the tubular passage 3 through the porous member 3d. As a result, a layer of inert gas is formed near the wall inside the tubular passage 3, and the part near the wall that is not turned into plasma is replaced by the inert gas, so that the diameter of the tubular passage 3 related to fine particles is substantially reduced. It's getting smaller. Therefore, fine particles can be produced while maintaining the above advantages without thermal deposition of the fine particles or damage to the tubular passageway 3.

In the one shown in FIG. 3, the raw material container side portion 3a of the tubular passage 3 has a small diameter comparable to that of the LIDB plasma P, the product container side portion 3b has a large diameter, and both portions 3a and 3c are connected with an O-ring 8. They are connected via A chamber portion 3e provided at the tip of the product container side portion 3b is supplied from a supply source (not shown).
The inert gas such as Ar supplied to the product container side portion 3b flows in a laminar flow state along the inner wall surface of the product container side portion 3b, replacing the portion near the wall surface that is not converted into plasma with the inert gas, and substantially converting the generation area of LIDB plasma P. The diameter is relatively small.

In the case shown in FIG. 4, the raw material container 1 is located above and the product container 2 is located below.
are connected by a tubular passage 3 extending vertically and having a structure similar to that shown in FIG. The LIDB plasma P is caused to flow down evenly along the inner wall surface of the product container side portion 3b surrounding the plasma, and the portion near the wall surface that is not converted into plasma is replaced with silicone oil, thereby making the generation area of LIDB plasma P substantially small in diameter. If the tubular passage 3 is made somewhat long, the fine particles can be collected in the silicone oil by utilizing thermal deposition of the fine particles on the wall surface.

The device shown in Fig. 1 mixes the raw material gases in the raw material container 1, so the raw material container 1 has a certain capacity, but several types of raw material gases are mixed in advance and supplied. In some cases, the raw material container 1 may have an extremely small capacity as shown in FIG. 5, or the raw material container may be omitted. Although not limited to the configuration shown in FIG. 5, in order to prevent particles in the source gas and generated fine particles from depositing on the window 5 and reducing the laser transmittance, As shown in FIG. 6, an injection port 9 is provided in an annular shape from the inside of the raw material container 1 toward the window 5, and an inert gas such as Ar is sprayed from the injection port 9 onto the window 5 to prevent particle deposition. You can also. In addition, if it is necessary to only prevent the generated fine particles from depositing on the window 5, use a lens 7 with a long focus so that the generation area of the LIDB plasma P is sufficiently separated from the window 5. The purpose can also be achieved.

Furthermore, when the raw material to be supplied has a high boiling point, the raw material can be once evaporated and condensed to generate a dust-containing air stream, and this can be supplied as the raw material gas. For example, as shown in FIG. 7, a high boiling point raw material A is heated in a raw material container 1 by a heater 10,
The material gas A is evaporated and condensed into fine particles of solid or liquid, carried on a carrier gas such as Ar or N ₂ supplied into the raw material container 1, and guided into the tubular passage 3. It can be mixed with another raw material gas B supplied into the tubular passage 3 earlier and reacted with the LIDB plasma P. In this case, the intermediate container for mixing raw material gas A and raw material gas B is LIDB.
It may be provided before the plasma P generation area. In addition, for heating the raw material A, in addition to the heater 10, a heating
Other means such as heating by irradiating with CO ₂ laser may also be used.

Furthermore, the means for collecting the generated fine particles is not limited to the one provided with the product container 2, but may also include a dust collecting device such as a cyclone, or cooling and collection of fine particles using a falling liquid film or shower. Furthermore, an adsorbent gas supply device for the purpose of surface modification of the generated fine particles may be attached.

Furthermore, in the embodiment, the laser beam focused by the lens 7 is made to enter the container through the window 5.
It is also possible to omit the window 5 and provide a lens 7 in the raw material container 1, so that the lens 7 also serves as a window.

In addition, the laser used for LIDB plasma generation is
Not only the CO ₂ laser but also other lasers can be used if various conditions are met.

Further, although the above-mentioned embodiments have shown that fine particles are generated from two or more types of raw material gases, the present invention
For example, it can be applied to generate metal fine particles by thermal decomposition of transition metal carbonyl, such as Ni(CO) ₄ → Ni+4CO. That is, Ni, Fe, Mo, W
It can be used as a new method of refining, in which metals and ores that react with CO to form carbonyl are first converted into carbonyl and then refined into fine metal particles. In addition, since the reaction of Ni(CO) ₄ mentioned above is extremely toxic, it is necessary to carry out the 8th reaction.
It is best to use a device like the one shown in the figure. That is,
Ni from raw material container 1 containing metal or ore
(CO) ₄ is thermally decomposed by LIDB plasma in the tubular passage 3, and the generated Ni particles are collected in the product container 2, and at the same time, the generated CO gas is circulated to the raw material container 1 through the pipe 11. TeNi
(CO) ₄ should be used to generate it, and the toxic gas should not leak outside.

Furthermore, the particle size distribution of the fine particles produced by the present invention is considered to be approximately lognormal distribution (self-preserving distribution) with a standard deviation of about 1.4, and the average particle size of the fine particles can be easily controlled. The invention can also be applied as a standard aerosol generator.

Furthermore, if the tubular passage 3 is made transparent,
It can also be applied as an emission spectrometer to analyze CVD reactions.

<Effects of the Invention> According to the present invention, fine particles with an extremely stable particle size can be produced from a wide range of raw materials using an extremely simple and easy-to-handle device, and the particle size can also be easily controlled. can.

Furthermore, thermal deposition of particles and damage to the tubular passage can be effectively prevented while maintaining the diameter of the tubular passage to be small without reducing particle generation efficiency.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a particulate production device according to an embodiment of the present invention, FIGS. 2 to 4 are construction diagrams each showing various aspects of the tubular passage, and FIG. Schematic configuration diagram showing the aspect of 6th
The figure is a block diagram showing the structure for preventing particle deposition on windows.
The figure is a schematic block diagram showing a fine particle manufacturing apparatus using high boiling point raw materials, and FIG. 8 is a schematic block diagram showing a fine particle manufacturing apparatus applied to the thermal decomposition reaction of Ni(CO) ₄ . In the drawing, 1 is a raw material container, 2 is a product container, 3 is a tubular passage, 6 is a laser oscillator, 7 is a lens, and P is
LIDB plasma.

Claims (1)

[Claims] 1. Guide a gaseous raw material into a tubular passage, irradiate laser light from a laser source along the axis of the tubular passage, and further focus the laser light within the tubular passage with a lens. In a particle manufacturing apparatus that generates dielectric breakdown plasma near a focal point and generates the raw material into fine particles through a thermally excited reaction caused by the dielectric breakdown plasma, using a porous member as the tubular passage,
A particle manufacturing device characterized in that an inert gas is sent into the passageway through the porous member. 2. Guide a gaseous raw material into a tubular passage, irradiate a laser beam from a laser source along the axis of the tubular passage, and further focus the laser beam within the tubular passage with a lens to create dielectric breakdown plasma near the focal point. In the particle manufacturing apparatus, an air chamber is formed on the upstream side of the tubular passage, and an inert gas is supplied from the air chamber to the inner wall surface of the passage. A device for producing fine particles characterized by flowing the particles along the same line. 3 Guide a gaseous raw material into the tubular passage, irradiate laser light from a laser source along the axis of the tubular passage, and further focus the laser light within the tubular passage with a lens to create dielectric breakdown plasma near the focal point. In the fine particle manufacturing apparatus, the raw material is generated into fine particles by a thermally excited reaction caused by the dielectric breakdown plasma, the tubular passage extends in the vertical direction, an oil chamber is formed in the upper part of the tubular passage, and the oil chamber A particulate production device characterized by causing silicone oil to flow down along the inner wall surface of a passage.